A computational fluid dynamics investigation of heat transfer and pressure drop characteristics of horizontal tubes with a coiled wire

In this study, the heat transfer and pressure drop effects for wire coil inserts in horizontal circular and square cross sectional tubes were examined by ANSYS FLUENT v17. Firstly, double helical wire coils with three different pitch (40, 60, and 80 mm) ratios inserted in a circular cross sectional pipe were investigated in the Reynolds number range between 16000 and 48000 under uniform constant wall temperature. The maximum pitch (80 mm) case showed the highest performance evaluation criteria (PEC=1.146) at minimum Reynolds number (17407). Secondly, three different cross sectional geometries of the wire with three different pitches in a square cross sectional tube were investigated to understand the thermo-hydraulic performance of them in the Reynolds number range of 4387 and 18415 under the uniform heat flux. The circular, triangular, and diamond cross sectional wire coils (CWC, TWC, and DWC, respectively) with 54, 72, and 90 mm pitches were tested. The Nusselt number of CWC, TWC, and DWC were higher than smooth pipe in the range of 38-88%, 37-93%, and 38-98%, respectively. Results showed that the maximum 30.46 % heat transfer enhancement was achieved in TWC group for the case of 90 mm. Finally, twisted tape and twisted tape with equilateral triangular wire coil in circular cross sectional pipe were investigated for 90 mm pitch in the Reynolds number range between 4600 and 21000 under uniform constant wall temperature. The difference in PEC between twisted tape and twisted tape with equilateral triangle cross sectional wire coil insert were in the range of 33 to 300%.